2006 design and construction of a two-axis sun tracking system for parabolic trough collector (ptc)

7/29/2019 2006 Design and Construction of a Two-Axis Sun Tracking System for Parabolic Trough Collector (PTC)

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Renewable Energy 31 (2006) 24112421

Design and construction of a two-axis Sun tracking

system for parabolic trough collector (PTC)

efficiency improvement

George C. Bakos

Laboratory of Energy Economics, Department of Electrical and Computer Engineering,

Democritus University of Thrace, 67 100 Xanthi, Greece

Received 5 October 2005; accepted 29 November 2005

Available online 23 January 2006

Abstract

An experimental study was performed to investigate the effect of using a continuous operation

two-axes tracking on the solar energy collected. The collected energy was measured and comparedwith that on a fixed surface tilted at 401 towards the South. The results indicate that the measured

collected solar energy on the moving surface was significantly larger (up to 46.46%) compared with

the fixed surface. The proposed two-axis Sun tracking system was characterized by a fairly simple

and low-cost electromechanical set-up with low maintenance requirements and ease on installation

and operation.

r 2005 Elsevier Ltd. All rights reserved.

Keywords: Solar energy; Two-axis tracking system; PTC efficiency

1. Introduction

Many authors have studied Sun tracking systems with different applications to improve

the efficiency of solar systems by adding the tracking equipment to these systems [16].

A tracking mechanism must be reliable and able to follow the Sun with a certain degree of

accuracy, return the collector to its original position at the end of the day or during the

night, and also track during periods of cloud cover. Fixed collectors producing heat or

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electricity throughout the year are usually installed and tilted at an angle equal to the

latitude of the installation site facing directly to the Sun. In this case, the energy collected by

the solar collector during both winter and summer is less due to Suns changing altitude.

The use of a tracking mechanism increases the amount of solar energy received by the solar

collectors resulting to a higher output power. Commercially, one-axis and two-axis trackingmechanisms are available. Usually, the single-axis tracker follows the Suns EastWest

movement, while the two-axis tracker follows also the Suns changing altitude angle.

The aim of this work is to present the installation of a two-axis Sun tracking system

which is based on the combined use of the conventional photoresistors and the

programming method of control which works efficiently in all weather conditions

regardless of the presence of clouds for long periods.

2. Automatic Sun tracking system design and control

The proposed Sun tracking system consists of the following parts [7]:

(i) the electro-mechanical movement mechanism,

(ii) the sensors signal processing unit, and

(iii) the system software.

2.1. Electro-mechanical movement mechanism

The electro-mechanical movement mechanism consists of four relays and two electroniccircuits, where the first is connected to the computer and the other to the sensors.

The four relays are connecting the motors to the electro-mechanical movement

mechanism, and their purpose is to move the solar collector reflector to four directions (up,

down, left and right).

The relays are driven through an electronic circuit which consists of eight similar sub-

circuits. Fig. 1 shows the schematic of one of those circuits.

The circuit operates for logic states 0 and 1. During the logic state 1, the current is

passing through the resistor R2 and the transistor Q1 is activated. Then, the relay closes

the circuit and the motor moves the reflector towards the desired direction. The all

movement procedure is controlled visually using the photodiode D2. Diodes D3 and D1protect the transistor and the circuit, respectively, from reversed polarity. During the logic

state 0, the transistor Q1 is deactivated and the relay opens the circuit.

The eight sub-circuits are divided in three groups and are described below:

The first group of sub-circuits consists of two sub-circuits used for the reflector

movements from left to right (EastWest) and are connected to the computer. The second

group of sub-circuits consists of two sub-circuits which are used for the reflectors movement

up and down (NorthSouth), connected also to the computer. The third group consists of

two sub-circuits for driving the reflector according to the sensors signal. There is also a sub-

circuit which connects the sensor system to the computer and another sub-circuit is used to

decide whether the sensors will be activated, depending on the level of solar intensity.Table 1 shows the possible combinations of resistors R2, R5, R8 and R11 logic states

(where resistors R5, R8 and R11 correspond to three remaining relay driving sub-circuits),

the corresponding states of the relays and the movements of the reflector.

ARTICLE IN PRESSG.C. Bakos / Renewable Energy 31 (2006) 241124212412


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The signals for the operation of the first and second group of sub-circuits are sent

through four of the eight output pins (D0D7) of the parallel port of the computer. The

other sub-circuits are operating autonomously.

2.2. Sensors signal processing unit

The sensors system consists of two photoresistors connected in series with voltage Uc.

When the resistors are facing the Sun then the voltage in the middle of the photoresistors is

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K1

RELAY SPDT

R2

2,2k

Signal

D3

DIODE

R11,5k

D1

DIODE D2LED

Q1NPN

+12V

R347k

Fig. 1. Sub-circuit for relay driving.

Table 1

Logic state combinations

Logicstate of

R2

Logicstate of

R5

Logicstate of

R8

Logicstate of

R11

Logic stateof relay for

horizontal

movement

(H1)


horizontal

movement

(H2)


vertical

movement

(V1)


vertical

movement

(V2)

State ofoperation

0 X 0 X 0 0 0 0 Idle

1 0 0 X 1 0 0 0 Left

movement

1 1 0 X 0 1 0 0 Right

movement

0 X 1 0 0 0 1 0 Up

movement0 X 1 1 0 0 0 1 Down

movement

Xno influence to system operation, 15 V DC/220 V AC, 00 V DC,0 V AC

G.C. Bakos / Renewable Energy 31 (2006) 24112421 2413


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Uc/2. Otherwise, the system is moving accordingly, so that the same value of resistance is

achieved in both photoresistors (Fig. 2). The comparison of resistor values is achieved

using the circuit shown in Fig. 3.

Outputs O1 and O2 of the triggers are connected to the relay control circuit which is

responsible for the movement of the reflector to the required directions. The sensor systemis operating when the solar radiation intensity exceeds a minimum level of solar intensity

(400 W/m2), and this is achieved with the circuit shown in Fig. 4.

2.3. System software

The system software is written in Visual C++ programming language, and the software

interface is shown in Fig. 5.

Manual operation of the reflector movement can be carried out activating the buttons

Motor 1 Left, Motor 1 Right, Motor 2 Up and Motor 2 Down. Using the buttons

Go To Left, Set Left End, Go To Down and Set Down End it is possible to pre-set theinitial position of the reflector during the beginning of the operation. The data given in the

windows Sun Rise, Sun Set, Sun Rise +301 and Sun Set 301 represent the Sun rise

time, the Sun set time and the time corresponding to 301 inclination of Sun in reference to

the horizon for the sunrise and sunset, respectively. Also, a graphical representation of the

reflector position is given. Finally, the user has the ability to select manually the sensors by

activating the Use sensor option.

When there is an interruption of power supply, the tracking system is switched off, and

when the system restarts the reflector orientation procedure begins automatically.

3. Description of the experimental facility

The metal frame (supporting structure) of the PTC consists of two fixed bases and three

moving parts (Fig. 6). The total length of the PTC frame is 6.10 m and the height is 8.60 m.

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R1 = R2 R1 > R2 R1< R2

R1R2 R1

R2 R1

R2

Fig. 2. Photoresistors set-up.

G.C. Bakos / Renewable Energy 31 (2006) 241124212414


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The dimensions of the parabolic reflector are 3.42 m in length and 3.24 m wide. One of the

moving parts is a pylon which is connected to one of the two fixed bases and has the ability

to move with respect to spherical coordinates (y,j). When the collector is in a horizontal

position, a small trolley can move on the pylon, from the lower point to the higher point,

forcing one end of the collector axis (pivot) to move upwards [8]. Since one end is fixed and

the length of the axis is constant, the pylon is changing position relative to the horizontalground. This movement can bring the axis of the PTC orthogonal to the incoming solar

radiation, and is necessary because the position of the Sun is changing according to the

season. The system also has the ability to follow the Suns daily orbit. This can be achieved

ARTICLE IN PRESS

U4C

74LS00

9

108

U4D

74LS00

12

1311

P9

4,7k

1

3

2

+

-

U2D

LM33911

1013

3

12

Uc

P4

51k

1 2

P5

51k

1

2

LDR3

+

-

U2C

LM3399

814

3

12

R27

2k

O3

Fig. 4. Circuit for the comparison of solar intensity level.

O1

LDR1

+

-

U1CLM339

9

814

3

12

P351k

1

2

P218k

1

2

UH2

+

-

U1DLM339

11

1013

3

12

U3A

74LS00

1

23

LDR2

R12k

Uf

U3D

74LS00

12

1311

C1100nF

R22k

UL1

UL2

U3B

74LS00

4

56

+

-

U1ALM339

7

61

3

12

O2

P151k

1

2

+

-

U1BLM339

5

4

2

3

12

U3C

74LS00

9

108

P74,7k

1

3

2

D1

Uc

UH1

Fig. 3. Circuit of four comparators and two RS triggers.



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by the EastWest rotation of the collector axis. These two movements can be achieved

using two AC Siemens motors. One of these motors (Fig. 7a) is 0.37 kW (1370 rpm) and is

being used for the vertical movement, and the other (Fig. 7b) is 0.75 kW (915 rpm) and isbeing used for the EastWest solar collector rotation. For both motors gearbox

MOTOVARIO is used, and the total time required for the collector to move from full

East to full West position is 540 s. The movement of the collector is protected using Philips

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Fig. 6. PTC supporting structure (metal frame).

Fig. 5. Interface for the control of reflector movement.



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end-point terminators. The large-scale parabolic base was installed in the industrial area of

Xanthi City in Greece.

Before the actual application of the Sun tracking system on the large-scale PTC

supporting structure, a small-scale PTC model was developed for laboratory experiments

and verification of reliable operation of the tracking system. This model is installed in theLaboratory of Energy Economics of Democritus University of Thrace and consists of two

metal bases and three moving parts. The PTC model is 1.37 m in length, 0.64 m wide and

1.34 m in height (Fig. 8).

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Fig. 7. (a) Motor for vertical movement. (b) Motor for horizontal movement.

Fig. 8. Small-scale PTC model.



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4. Experimental results and discussion

The experiments were carried out in the industrial area of Xanthi where the large scale

parabolic mirror base was installed. For the measurements two pyranometers were used.

One was placed in the center of the parabolic mirror base and the other on a 401 fixedsurface facing the South. The results were normalized in order to compare the pyranometer

readings easily and also to compensate for reading fluctuations. The maximum intensity of

global solar radiation noticed during the experiments was 1010 W/m2 and measured

between 14:3015:30 on 1 June 2004.

Two sets of experiments were carried out in order to assess the efficiency of the proposed two-

axis tracking system. One set of measurements was taken under normal weather conditions

(absence of clouds and rain) running on combined software and sensor mode of operation. The

other set of measurements was taken under abnormal weather conditions running firstly on

combined software and sensor mode of operation and secondly only on software mode.

4.1. Measurements of two-axis tracking system under normal weather conditions

(i) The experiments took place on 12 May 2004 from 06:30 to 19:30 PM and the ambient

temperature was 22 1C, the humidity 45%, and the results are shown in Fig. 9. During

these experiments the weather conditions were very good and there were no clouds in

the sky.

(ii) The experiments took place on 1 June 2004 from 06:30 to 19:30 with ambient

temperature 25 1C, the humidity 50%, and the results are shown in Fig. 10. During

these experiments the weather conditions were very good and there were almost noclouds in the sky.

(iii) The experiments were carried out on 20 April 2004 from 06:30 to 19:30, the ambient

temperature was 23 1C and the humidity 50%. During the experiment the weather

conditions were very good and there were almost no clouds in the sky. The

experimental results are shown in Fig. 11.

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0.0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

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1.0

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0

8:0

0

9:0

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0

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0

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19:3

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20:0

0

Time (Hours:Min)

NormalizedSolarRadiationV

alues

Fixed

Two axis tracking

Fig. 9. Experimental results using combined software and sensors mode of operation.



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From the experimental results (i), (ii), and (iii), it can be noticed an increased efficiency

of the two-axis tracking due to the variation of Sun orbit (NorthSouth and EastWest

movement). The efficiency is improved when the Sun inclination is increased with respect

to 401 inclination of fixed surface and, in any case, when the parabolic collector base istracking EastWest, particularly during early morning and late afternoon hours. The

solar energy collection efficiency of the PTC, due to the application of the developed

tracking system compared to fixed surface inclination, is given in Table 2.

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0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

7:00

8:00

9:30

10:30

11:30

12:30

13:30

14:30

15:30

16:30

17:30

19:00

20:00

Time (Hours:Min)

NormalizedSolarRadiationValues

Fixed

Two axis tracking


0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

0.9

1

7:00

8:00

9:00

10:30

11:30

12:30

13:30

14:30

15:30

16:00

17:00

18:00

19:00

Time (Hours:Min)

NormalizedSolarRadiation

Values

FixedTwo axis tracking




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4.2. Measurements of two-axis tracking system under abnormal weather conditions

(i) The experiments took place on 2 June 2004 from 09:45 to 17:00 with ambient

temperature 19 1C and 50% humidity, and the results are shown in Fig. 12. During the

experiment the solar radiation after the noon hours was decreased due to the

appearance of clouds and rain (marked by the arrow) in late afternoon hours.It can be seen that after the decrease of solar radiation intensity, the developed

software is helping the reflector to follow the Sun up to the end of the day, even though

the solar intensity is inadequate to switch on the sensors.

(ii) The experiments took place on 18 July 2004 from 09:45 to 17:00 with ambient

temperature 26 1C, 40% humidity, and the results are shown in Fig. 13. As it can be

noticed during late afternoon hours, the solar radiation intensity decreases due to rain

(pointed by the arrow) although the rest of the day the weather is quite good.

5. Conclusions

In this paper an experimental study is performed to investigate the effect of two-axis

tracking on the solar energy collected under normal and abnormal weather conditions.

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Table 2

Experimental average daily total solar radiation in MJ/m2

Date Two axis tracking (MJ/m2) Fixed at 401 latitude (MJ/m2) Gain (%)

20-04-04 34.07 23.52 44.86

12-05-04 35.76 24.55 45.66

01-06-04 38.15 25.63 48.85

Average 35.99 24.57 46.46

0

0.1

0.2

0.3

0.4

0.5

0.60.7

0.8

0.9

1

1

0:00

1

0:30

1

1:00

1

1:30

1

2:00

1

2:30

1

3:00

1

3:30

1

4:00

1

4:30

1

5:00

1

5:30

1

6:00

1

6:30

1

7:00

Time (Hours:Min)

NormilizedSolarRadiatio

nValues

Fixed

Two axis tracking




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Experimental results based on different modes of system operation are presented. It is

concluded that when the solar intensity is low and the tracking system operates only on

sensor mode, the solar reflector cannot follow the Sun orbit, and the efficiency is decreased

significantly, reaching the efficiency of the fixed inclination surface. However, in this case

the tracking system behavior is improving considerably when it operates on combinedsoftware and sensor mode. The developed tracking mechanism could be used efficiently to

orient other concentrating solar collectors such as parabolic dish collectors.

The gain of the proposed two-axis tracking system is considerable (up to 46.46%)

compared with the fixed surface for operation under normal weather conditions. Further

studies are already in progress to evaluate the integration of the proposed system in specific

solar thermal and photovoltaic applications in Greece.

References

[1] Kalogirou SA. Design and construction of a one-axis Sun-tracking system. Solar Energy 1996;57(6):4659.[2] Abdallah S. The effect of using Sun tracking systems on the voltagecurrent characteristics and power

generation of a flat plate photovoltaics. Energy Convers Manage 2004;45:16719.

[3] Khalifa A, Al-Mutawalli S. Effect of two axis Sun tracking on the performance of compound parabolic

concentrators. Energy Convers Manage 1998;39(10):10739.

[4] Al-Mohamad A. Efficiency improvements of photo-voltaic panels using a Sun-tracking system. Appl Energy

2004;79:34554.

[5] Abdallah A, Nijmeh S. Two axes Sun tracking system with PLC control. Energy Convers Manage

2004;45:19319.

[6] Kalogirou S. Design of a fuzzy single-axis Sun tracking controller. Int J Renew Energy Eng 2002;4(2).

[7] Lianopoulos E. Development of a two-axis tracking system for PTC used for solar energy conversion to

electricity. MSc thesis, Democritus University of Thrace, Xanthi, 2004 [in Greek].

[8] Bakos GC, Ioannidis I, Tsagas NF, Seftelis I. Design, optimisation and conversion-efficiency determination ofa line focus parabolic-trough solar-collector (PTC). Appl Energy 2001;68:4350.

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Fig. 13. Experimental results using only sensor mode of operation without software support.


2006 design and construction of a two-axis sun tracking system for parabolic trough collector (ptc)

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